It is well known to join plural parts together to form structural members. More particularly, it is known to utilize separately formed body panel members to form enclosures such as operators cabs for work vehicles and the like. These body panel members are frequently compression molded or rotationally molded from thermoplastic or thermoset materials. Such panels are then joined together to form structural members such as roofs or sidewalls, so as to provide a strong, durable structure which may have wiring, insulation, ventilation ducts etc. installed between the panels. In the construction of such structures it is frequently necessary to employ some type of seal between the panels to limit the movement of air and/or entry of moisture so as to provide a desired level of weather-proofing. The use of liquid or semi-liquid mastic sealant is well known for such purposes. Typically the panels will be formed having a tongue-in-groove or similar configuration at the joint location, into which a sealant is introduced prior to the panels being joined. One major drawback of such methods is that when the parts are joined the sealant is compressed and a certain amount of sealant is squeezed out of the joint. In the construction of vehicle body panels in particular, it is undesirable to have sealant protruding out from the joint in areas where it can be seen. For example, in the construction of a two-piece roof member it may be acceptable to have sealant protruding from the joint on the inside of the roof structure i.e. between the panels where it cannot be seen, but it is undesirable to have the sealant protruding from the joint on the outside which is visible to the end user of the product. Accordingly, there is a clear need in the art for a joint design which limits the amount of excess sealant that is squeezed out of the joint on the visible side of the structure by directing the flow of excess sealant in one direction.